[nazgul17]

If it were walking what keeps Asians slim, you'd see more variation, imo. The small portions and generally healthier food are what keeps them slim. True that the Japanese eat fried chicken and cakes, but not as often as Americans, and not as much each time.

[washadjeffmad]

There's a certain positive status associated being "fat and happy" in the US.

Americans are also, on the whole, gigantic people. Tall, wide, huge frames and/or a lot of meat on the bone. Only some of that is accounted for by diet.

I think there's more to do in Japan locally, or at least more general social/physical freedom, which I attribute to low costs and high mobility. Nature in the US is generally privatized, far out of the way, or has limited access or parking. If you travel by walking in the US, middle class people think you're poor or your car has broken down. There's a bit of a stigma in some cases and places against not being sedentary and large (or, having to move and sweat for anyone).

[deprecative]

It's really quite simple to me. I don't quite understand why folks seem to argue about why the US is obese and Japan isn't. It comes down to one thing but I suspected aided by another three things:

In Japan a mindset of just enough seems to be prevalent. They do not seem to be as prone to glorifying excess in all ways like us Americans tend to be. I think this is a / the key aspect which is supported by these:

Americans are not active. Japanese people tend to be active and walking absolutely contributes to this.

Americans eat low quality food. We eat a lot of food with added sugar. We feed candy to children in sugary water-fat for breakfast. We eat processed and ultra processed foods regularly even when we primarily prepare meals at home.

Americans are anti-conformist. Japan is very conformist. This relates to social pressure(fat shaming, diet) and social activity cohesion (exercise, dieting).

It seems quite evident at even a glance why one country would be overweight while the other tends to be fit. In the US our culture rewards excess. We value cars more than people. We care about profits over people, too, really. Things like healthcare and food come to mind here.